WASHINGTON - A new wave of children born to Mexican immigrants in the United
States could find it increasingly difficult to assimilate, an immigration
research group concluded in a report released Thursday.

The Center for Immigration Studies, a 20-year-old spin-off of the Federation for
American Immigration Reform - an anti-immigration lobbying group - also used the
report to press for a crackdown on undocumented workers.

"The present situation and the immediate future are without precedent," said
report author Steven Camarota, the center's research director.

Some 23 percent of all 2002 births in the United States were to foreign-born
mothers, according to the group's report. Of those births, 42 percent were to
illegal-immigrant mothers, the center estimated.

The number of illegal immigrants inside the United States is unknown, but most
estimates peg it at 8 million.

Camarota said the Center for Immigration Studies calculated the
illegal-immigrant birth rate from its own estimates, which were based on 2000
Census Bureau data.

The Census Bureau does not inquire about immigration status in surveying, but
asks for respondents' citizenship status, year of arrival in the U.S., country
of birth and other information.

Regardless of the exact numbers, illegal immigration is increasing the U.S.
labor supply and "making the poor poorer, costing taxpayers a lot of money and
reducing productivity," Camarota said.

Camarota said that according to his research, there is already an ample supply
of unskilled labor in the U.S.

"Either you're going to enforce the law or you're going to start handing out
green cards," he said.

Granting temporary legal status to immigrant workers - a plan under
consideration on Capitol Hill - would result in "millions of permanent additions
to the U.S. population," Camarota said.

Ten percent of U.S. births in 2002 were to Mexican-born mothers, up from 1.5
percent in 1970.

"No country has ever accounted for such a large share of immigrant births as
Mexico does today," Camarota said.

Living in ever-larger immigrant communities, these children face less pressure
than previous generations to assimilate, Camarota said.

"In that regard, we are headed into uncharted territory," Camarota said.

Pro-immigration groups reject Camarota's arguments.

"Their statistics are largely irrelevant," said Walter Ewing, a research
associate at the Immigration Policy Center.

Ewing said the Center for Immigration Studies' report bears an eerie resemblance
to the kind of rhetoric that was used 100 years ago to oppose waves of
immigrants from eastern and southern Europe.

"Successive generations of immigrants, from parents to children to
grandchildren, have always improved their levels of income," Ewing said.